Photomask and exposure method

ABSTRACT

A photomask illuminated with an exposure illuminating light having a short wavelength of, e.g., about 200 nm or less and having an improved uniformity of transmittance distribution. On one surface (B) of a flat substrate ( 1 ) made of quartz, a quartz glass, or a quartz glass to which a predetermined impurity is added, a thin film ( 3 ) made of a material semitrasparent to the exposure illuminating light. The transmittance distribution for the illuminating light of the substrate ( 1 ) is measured prior to the formation of the thin film ( 3 ), and the distribution of the thickness of the thin film ( 3 ) is determined so as to compensate the unevenness of the transmittance distribution. An original pattern ( 2 ) is formed on the opposed surface (A) of the substrate ( 1 ) to the surface (B).

This application is the national phase under 35 U.S.C. §371 of prior PCTInternational Application No. PCT/JP99/03484 which has an Internationalfiling date of Jun. 29, 1999 which designated the United States ofAmerica, the entire contents of which are hereby incorporated byreference.

TECHNICAL FIELD

The present invention relates to a photomask used in a lithographyprocess for producing fine patterns of electronic devices such assemiconductor integrated circuits, image pickup devices (CCDs etc.),liquid crystal displays and thin film magnetic heads, and the presentinvention also relates to an exposure method using this photomask. Thepresent invention is preferably used when light having a wavelength ofabout 200 nm or less is used as illumination light for exposure.

BACKGROUND ART

Conventionally, in a lithography process for forming a fine pattern ofan electronic device such as a semiconductor integrated circuit and aliquid crystal display, there is used a method in which a reticle as aphotomask on which an original pattern obtained by enlarging a patternto be formed four to five times is disposed on a projection exposureapparatus, and under predetermined illumination light for exposure(exposure light), the original pattern is reduced in size and projectedand transferred onto a wafer (or glass plate or the like) as a substrateto be exposed on which a photoresist is applied.

When such a pattern of the reticle is transferred, a line width of theresist pattern formed on the wafer after development is increased orreduced in accordance with integrated exposure amount of the exposurelight with respect to the wafer. Thereupon, in order to obtain adesigned line width over the entire surface of the resist pattern, theillumination distribution of the exposure light to the pattern of thereticle is maintained uniform extremely precisely so that an error ofthe distribution is in a range of, for example, +1% within theillumination region.

In the projection exposure apparatus, in order to enhance resolution tomeet finer semiconductor integrated circuits, wavelength (exposurewavelength) of the exposure light tends to be shorter. At the present,248 nm of a KrF excimer laser becomes mainstream as the exposure lightwavelength, but 193 nm of an ArF excimer laser having shorter wavelengthwill soon be in practical use. Further, research has been conducted todevelop a projection exposure apparatus using an F₂ laser having shorterwavelength (wavelength is 157 nm).

If the exposure light wavelength is in vacuum ultraviolet region (VUVregion) of wavelength of about 200 nm or less, e.g., 157 nm by the F₂laser, kinds of preferable materials as substrate material of thereticle which allow exposure light of such short wavelength to passtherethrough are limited. For example, fluorite (calcium fluoride) hasexcellent transmissivity at that wavelength, but since the linearexpansion coefficient is as great as about 20×10⁻⁶/K, the fluorite isnot always preferable as the substrate material of reticle. With such agreat linear expansion coefficient, the substrate of the reticle isexpanded by the illumination heat of the exposure light generated whenthe exposure and transfer, and the positional precision of a pattern tobe transferred is deteriorated. Therefore, in order to use the fluorite,it is necessary to enhance the cooling function of the reticle forexample.

As explained above, in the projection exposure apparatus, the exposurelight wavelength tends to be shorter, but if the exposure lightwavelength becomes about 157 nm, there is conventionally almost nomaterial for the substrate of the reticle having high transmissivity andrelatively small linear expansion coefficient.

In this regard, an attempt to use quartz and a synthetic quartz (quartzglass) doped with fluorine as the substrate material which issubstantially transparent with respect to light of wavelength of about157 nm has been made.

However, also with respect to the quartz and the quartz glass doped withfluorine, the wavelength of about 157 nm is close to the absorbing end(wavelength from which material-inherent abrupt absorption starts) oflight for each material, and there is an adverse possibility that thetransmissivity distribution of the material is largely varied at thewavelength near 157 nm due to slight non-uniformity in composition ofthe material, stress deformation generated in the material or the like.Due to these factors, if the transmissivity distribution inside thereticle substrate becomes uneven (non-uniformity), the uniformity inline width of the resist pattern to be transferred onto the wafer isdeteriorated as in the case in which the illumination distribution ofthe exposure light for illuminating the reticle becomes non-uniform. Thedeterioration in uniformity in line width of the resist pattern bringsabout non-uniformity in circuit line width in an electronic device to beproduced, which largely deteriorates operating speed of the electronicdevice for example.

In view of the above circumstances, it is a first object of the presentinvention to provide a substrate for a photomask having highly uniformtransmissivity distribution and to provide the photomask.

It is a second object of the invention to provide a substrate for aphotomask having a. relatively high transmissivity with respect to lightof short wavelength of about 200 nm or less, for example, and having auniform transmissivity distribution, and to provide the photomask.

It is a third object of the invention to provide an exposure method anda producing method of a device capable of producing an advanced deviceusing the photomask.

Disclosure of the Invention

A substrate for a photomask according to the present invention is asubstrate for a photomask on which an original pattern is formed, andthe substrate is provided with a transmisslvity compensating memberwhich compensates for non-uniformity of a transmissivity distributioninside the substrate.

According to the present invention, if the photomask is irradiated withexposure illumination light (exposure light) of a predeterminedwavelength, a reduction amount of the transmissivity by thetransmissivity compensating member is reduced in a portion of thesubstrate where the transmissivity of the substrate itself is lower thanthe average value under that wavelength, and the reduction amount of thetransmissivity by the transmissivity compensating member is increased ina portion of the substrate where the transmissivity of the substrateitself is higher than the average value. With this arrangement, thenon-uniformity of the transmissivity distribution of the substrate iscompensated, and it is possible to secure sufficiently high uniformityof the transmissivity distribution to be used as a substrate for thephotomask.

In this case, it is preferable to. form the substrate of quartz, quartzglass (e.g., synthetic quartz glass having hydroxyl (OH group) ofconcentration of 1000 ppm or more), quartz glass doped with apredetermined impurity (e.g., fluorine (F₂) or the like), sapphire(Al₂O₃) or magnesium fluoride (MgF₂). These materials have relativelyhigh transmissivity even in vacuum ultraviolet region of wavelength ofabout 200 nm or less, and since the quartz to the sapphire have linearexpansion coefficient smaller than that of fluorite, the quartz to thesapphire are suitable as the substrate of the photomask which isirradiated with exposure light of such short wavelength. The magnesiumfluoride can allow light of shorter wavelength to pass through ascompared with the fluorite.

One example of the transmissivity compensating member is a thin filmprovided on one surface of the substrate, and a film thicknessdistribution of this thin film is set in accordance with thetransmissivity distribution of the substrate. In this case, thetransmissivity distribution of the substrate can be compensated only bycontrolling the film thickness distribution.

The transmissivity compensating member may be formed by reforming, in atleast one surface of the substrate, a vicinity of the one surface of thesubstrate, or the transmissivity distribution may be formed by providinganother substrate other than the substrate with a transmissivitydistribution which substantially compensates for the non-uniformity ofthe transmissivity distribution of the substrate.

Next, a first photomask according to the present invention is aphotomask which includes a substrate having a thin film as thetransmissivity compensating member, and an original pattern is formed ona surface of the substrate opposed to a surface on which the thin filmis formed. With this arrangement, the original pattern can be formedwithout being affected by the transmissivity compensating member.

A second photomask according to the present invention is a photomaskwhich has a substrate provided with the transmissivity compensatingmember according to the invention, and the original pattern is formed onone surface of the substrate. As this photomask, a mask having asubstrate doped with a predetermined impurity with such a distributionas to compensate for transmissivity distribution of the substrate itselfis included.

It is preferable that a line width of at least one portion of theoriginal pattern is different from the designed value in accordance withthe transmissivity distribution of the substrate provided with thetransmissivity compensating member.

In the present invention, the designed value is a value obtained bymultiplying a size of a pattern to be formed on a photosensitive objectby a reciprocal of projection magnification of a projection opticalsystem when the original pattern of the photomask is transferred ontothe photosensitive object through the projection optical system. Whenthe original pattern (including both dense pattern and isolated pattern)is transferred onto the photosensitive substrate, if the line width ofthe pattern to be actually formed on the photosensitive substratebecomes thin or short with respect to a size value of a pattern to beformed on the photosensitive substrate, the size value of the originalpattern is increased or reduced to correct to compensate the variationamount in some cases, and a value after the correction is also includedin the designed value of the invention.

Next, in a third photomask according to the present invention, anoriginal pattern is formed on the substrate and in order to compensatefor the non-uniformity of the transmissivity distribution inside thesubstrate, a line width of each pattern in the original pattern ischanged in accordance with the transmissivity distribution of thesubstrate. With this photomask, in a portion thereof where thetransmissivity of the substrate itself is lower than the average valuefor example, the line width of a light-shield pattern in the originalpattern is made thinner than the designed value, and in a portion wherethe transmissivity of the substrate itself is higher than the averagevalue, the line width of the light-shield pattern is made thicker thanthe designed value. With this arrangement, the transmissivitydistribution of the photomask is uniformized.

Next, in a first exposure method according to the present inventionwhich illuminates a photomask to expose a photosensitive object withlight passing through an original pattern of the photomask, thesubstrate is provided with a transmissivity compensating member in orderto compensate for non-uniformity of a transmissivity distribution insidea substrate of the photomask. That is, the first or second photomask ofthe present invention is used.

In a second exposure method according to the present invention whichilluminates a photomask to expose a photosensitive object with lightpassing through an original pattern of the photomask, in order tocompensate for nonuniformity of a transmissivity distribution of thephotomask, an illumination distribution of light on the photosensitiveobject is adjusted in accordance with the transmissivity distribution.

With the second exposure method of the present invention, theillumination distribution of the light on the photosensitive object isadjusted in accordance with the transmissivity distribution of thephotomask, and the uniformity of the illumination distribution of thelight on the photosensitive object is enhanced, thereby improving theuniformity of the line width of the pattern formed on the photosensitivematerial.

In a third exposure method according to the present invention whichilluminates a photomask to expose a photosensitive object with lightpassing through an original pattern of the photomask, in order tocompensate nonuniformity of a transmissivity distribution inside asubstrate of the photomask, a line width of each pattern in the originalpattern is changed in accordance with the transmissivity distribution ofthe substrate. With this arrangement, the third photomask of theinvention is used.

Next, a first device producing method in accordance with the presentinvention comprises transferring a device pattern onto a substrate for adevice using the exposure method of the present invention. A second,third or fourth device producing method according to the presentinvention is a device producing method for producing a predetermineddevice using the first, second or third photomask of the presentinvention, and comprises exposing an original pattern on the substrateonto a device substrate by illuminating the photomask with illuminationlight passing through the substrate. The uniformity of thetransmissivity distribution of the photomask according to the presentinvention is extremely high and therefore, the uniformity of the linewidth of the circuit pattern of the device formed on the substrate isenhanced, and an advanced device can be produced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plan view showing a reticle according to a first embodimentof the present invention;

FIG. 1B is a sectional view taken along a line AA in FIG. 1A ;

FIG. 2 is a schematic block diagram showing an essential portion of ameasuring system for measuring a transmissivity distribution of thesubstrate 1 of the reticle shown in FIGS. 1A and 1B;

FIG. 3 is a view showing an essential portion of a film formingapparatus for forming a thin film on a surface B of the substrate;

FIG. 4 is a plan view showing a reticle according to a second embodimentof the present invention; and

FIG. 5 is a perspective view showing an essential portion of aprojection exposure apparatus in which the reticle R in FIGS. 1A and 1Bis used to perfonn exposure.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be explained. First,a first embodiment will be explained with reference to FIGS. 1 to 3.

FIG. 1A is a plan view showing a reticle R as a photomask of thisembodiment, and FIG. 1B is a sectional view taken along a line A—A inFIG. 1A . As shown in FIGS. 1A and 1B, an original pattern 2 is formedon a one surface (pattern surface) A of a substantially square flatsubstrate 1 which is transparent with respect to light having wavelength(exposure wavelength) of exposure illumination light for illuminatingthe reticle R. A thin film 3 having film thickness distribution suitablefor transmissivity distribution of the substrate 1 is formed on asurface (back surface) B opposed to the surface A in order to compensatenon-uniformity of the transmissivity distribution of the substrate 1.This thin film 3 corresponds to a transmissivity compensating member ofthis invention. Contour lines HI to H4 are curves connecting points ofthe thin film 3 having the same thickness, and in the reticle R of thisembodiment, the thickness of the thin film 3 is increasing toward thecenter of the reticle R. That is, in the thin film 3, a portion (centralportion) “a” thereof surrounded by the contour line H1 is most thick,and portions “b”, “c” and “d” become thinner in this order.

The thin film 3 is made of semitransparent material havingtransmissivity in some degree with respect to exposure wavelength whenthis reticle R is used, and the transmissivity can be controlled inaccordance with the film thickness. In the case of FIGS. 1A and 1B, thetransmissivity with respect to the exposure wavelength of the substrate1 itself is higher at its center, and becomes lower toward the peripheryor outer side of the substrate 1. Therefore, in order to compensate thisnon-uniformity to realize uniform transmissivity over the entire surfaceof the reticle R, the film thickness distribution as shown with thecontour lines H1 to H4 is set.

Here, if it is assumed that the exposure wavelength is 157 nm, examplesof materials of the substrate 1 are quartz, synthetic quartz (quartzglass) added (doped) with a predetermined impurity such as fluorine(F₂), and quartz glass having hydroxyl (OH group) of concentration of1000 ppm or more. As the material of the substrate 1 of the reticle R, amaterial which is not transparent with respect to the exposurewavelength, e.g., a common synthetic quartz when the exposure wavelengthis 157 nm can be made thinner (about 2 mm or less) than a normal case(about 6 mm) for use.

As the quartz as the material of the substrate 1, i.e., as the quartzwhich is crystallized into a predetermined state, a synthetic quartzproduced (incubated) by a hydro-thermal method for example can be used.Since the synthetic quartz has excellent transmissivity with respect toultraviolet rays of wavelength up to 146 nm, the synthetic quartz hassufficient transmissivity with respect to the exposure light of 157 nmof the F₂ laser. When the quartz is used as the material of thesubstrate 1, it is preferable that the pattern surface A onto which theoriginal pattern 2 shown in FIG. 1B is formed is set parallel to anoptical axis (Z axis or c axis) of the quartz. This is because thatsince the linear expansion coefficient of the quartz is about1.337×10⁻⁵/K in a direction (X axis or a axis, Y axis or b axis)perpendicular to the optical axis and about 0.797×10⁻⁵/K in thedirection of the optical axis, it is advantageous to set the directionhaving greater linear expansion coefficient into a thin direction, andthe direction having smaller linear expansion coefficient. i.e., theoptical direction into a direction along the large pattern surface. Withthis arrangement, when the reticle pattern is formed and when wafer isexposed. adverse effect due to the thermal expansion of the substrate 1is reduced, and it is possible to enhance the formation precision of thereticle pattern and to enhance the formation precision of the circuitpattern on the wafer.

The linear expansion coefficient of the quartz is about ½ to ⅓ or lessas compared with the fluorite, the thermal expansion amount of thequartz is smaller than that of the fluorite.

Even if the quartz is a synthetic quartz, it is possible to obtainsubstantially the same as or more excellent transmissivity than that ofa natural quartz. For example, the content of hydroxyl of the naturalquartz is 4 ppm and wavelength capable of passing through the quartz is152 nm, values of the synthetic quartz are varied, and the bestsynthetic quartz has the content of hydroxyl is likewise 4 ppm and thewavelength capable of passing through the quartz is about 146 nm.Therefore, even the exposure light is the F₂ laser light (wavelength is157), the synthetic quartz has excellent transmissivity.

Next, as a producing method of a synthetic quartz (“fluorine-dopedquartz glass”, hereinafter) doped with fluorine (F₂) used as thesubstrate 1, a method disclosed in Japanese Patent Application Laid-openNo.H8-67530 can be used. According to this method, a silicon compoundsuch as SiCl₄ is hydrolyzed in hydrogen flame by a VAD (Vapor PhaseAxial Deposition) method to obtain glass fine particles. Next, the glassfine particles are deposited to form a porous glass. A formation methodand a condition of the porous glass are not limited, and a so-called OVD(Outside Vapor Deposition) or so-called sol-gel method or the like.inaddition to the VAD method may be employed.

Then, the porous glass is heated in atmosphere including fluorinecomprising SiF₄/He for example to obtain porous glass doped withfluorine.

The fluorine-doped synthetic quartz glass is heated in atmosphereincluding hydrogen glass to obtain a synthetic quartz glass doped withthe fluorine and hydroxyl (OH group).

In this embodiment, OH group is doped in addition to fluorine in thismanner, and this enhances the transmissivity of the substrate. Theconcentration of fluorine is preferably about 1 to 5% by weight, and theconcentration of OH group is preferably about 100 ppm to 1000 ppm.

In addition to fluorine, about 1×10¹⁷ molecules/cm³ to 1×10¹⁰molecules/cm³ may be doped. By doping hydrogen also, it is possible toremarkably enhance the ultraviolet resistance by synergism ofcharacteristics with respect to the ultraviolet resistances of fluorineand hydrogen molecules.

A common substrate at present has a thickness of about 6 mm and a sizeof about 150×150 mm, and the producing method such as the VAD method,the OVD method and the sol-gel method are suitable of a columnar quartzglass, and are not suitable for producing a flat glass having such alarge area. Thereupon, when the quartz glass substrate is produced, itis possible to employ such a method that a columnar glass rod isproduced by any of the above methods and then, the columnar glass rod isdeformed into a substantially flat plate-like shape by heating press andthen, the flat glass is formed into a desired size by grinding andpolishing. At the time of press deformation, the glass maybe subjectedto hydrogen atmosphere treatment at 500° C. after the heatingprocessing. With this method, it is possible to produce a substrate of alarge reticle of 230 mm (9 inches)×230 mm.

With the above method, a reticle substrate of 150×150 mm or 230×230 mmcan be formed from a columnar quart glass having small diameter, and itis possible to produce a reticle of this embodiment by a smaller, i.e.,more inexpensive production facilities. Further, since the linearexpansion coefficient of quartz glass is as small as about 0.5×10⁻⁶/K,the thermal expansion amount at the time of working and exposure, and ifa reticle using the quartz glass as substrate is used, precision of linewidth and the like of the circuit pattern to be formed on a wafer islargely enhanced.

Further, a producing method of the substrate 1 using the syntheticquartz glass whose OH group concentration is 1000 ppm or more will beexplained. A synthetic quartz glass used for producing the substrate 1in this case is a synthetic quartz glass whose structure determinationtemperature is 1200 K or less and whose OH group concentration is 1000ppm or more, more preferably, 1000 to 1300 ppm.

By setting the OH group concentration to 1000 ppm or more and structuredetermination temperature to 1200 K or less, when the glass is appliedto vacuum ultraviolet rays having wavelength of about 200 nm or less,scattering loss and absorbing loss can be reduced to extremely lowlevel, and deterioration with time can be reduced. Therefore, byproducing the substrate 1 using such a synthetic quartz glass, it ispossible to obtain a reticle R having high transmissivity and excellentultraviolet resistance.

Next, examples of materials of the thin film 3 as the transmissivitycompensating member are oxide such as silicon dioxide (SiO₂) andaluminum oxide (A1 ₂O₃), and fluoride such as magnesium fluoride (MgF₂)and aluminum fluoride (AlF₃). In order to obtain necessary absorptivity,an absorbent impurity such as metal like chromium (Cr) may be added. Inthis case, oxide such as silicon dioxide and aluminum oxide is stablewith respect to acid such as sulfuric acid which is cleaning liquid usedfor cleaning reticles using the oxide, the oxide is excellent as amaterial of the thin film 3. On the other hand, if fluoride is used asthe material of the thin film 3, there is merit that the presentinvention can be applied also to shorter exposure wavelength by thecharacteristics of transmissivity.

A metal thin film such as chromium and aluminum may be used as thematerial of the thin film 3. In this case, since illumination light isreduced mainly by reflection, an absorbance amount of the thin film 3itself is only a slight amount, and there is merit that durability atthe time of irradiation is excellent.

In FIG. 1B although the thickness of the thin film 3 is illustrated verythick with respect to a thickness (usually about 6 mm) of the substrate1 of the reticle so as to emphasize variation over the entire surface ofthe thin film 3, the actual thickness of the thin film 3 is as small asabout some 100 μm or less.

In the above embodiment, it is assumed that the wavelength is 157 nm,but it is apparent that the present invention can also be applied whenexposure light having long wavelength such as the ArF excimer laser(wavelength is 193 nm) or exposure light such as the Ar₂ laser light(wavelength 126 nm) shorter than 157 nm or the Kr₂ laser light(wavelength is 147) are used. When exposure light of wavelength shorterthan 157 nm, fluorite (CaF2), magnesium fluoride (MgF₂) or the like canbe used as a material of the substrate 1. When the fluorite is used asthe substrate of the reticle, since the fluorite has great linearexpansion coefficient, it is preferable to maintain a temperature of thereticle as constant as possible by a method for circulating gas(nitrogen, helium or the like) whose temperature is adjusted to apredetermined level.

Sapphire (A1 ₂O₃) can be a material which can be used even if thewavelength is about 200 nm or less. Since the linear expansioncoefficient of the sapphire at a room temperature is about 8×10⁻⁶/Kwhich is smaller than that of the fluorite, the effect of thermalexpansion is small.

The material of the substrate 1 is not limited to the above-describedsubstances, and the material may be selected in accordance with thetransmissivity with respect to the exposure wavelength. The material ofthe substrate 1 may be the same and doped impurity or producing methodof the substrate 1 may be different. That is, in the present invention,the material of the substrate 1, the presence or absence of additive,kind of additive and a producing method of the substrate 1 are notlimited, and any material, additive and producing method may be usedonly if the optical characteristics (including transmissivity, linearexpansion coefficient and the like) required as a photomask (reticle) issatisfied.

Next, one example of the producing method of the reticle of theembodiment will be explained using FIGS.2 and 3.

FIG. 2 is a schematic block diagram showing an essential portion of ameasuring system for measuring a transmissivity distribution of thesubstrate 1 itself of the reticle R shown in FIGS. 1A and 1B. In FIG. 2,a light pencil L1 emitted from a light source 4 having substantially thesame wavelength as the exposure wavelength branches by a half mirror 5,the substrate 1 is irradiated with branched one light pencil L2, and theother light pencil L3 enters an optoelectronic detector DB. A lightpencil Light source 4 which has passed through the substrate 1 enters anoptoelectronic detector DA. A photodiode, photo-multiplier and the likecan be used as the optoelectronic detectors DA and DB. Outputs(optoelectronic conversion signals) SA and SB are supplied to a signalprocessing system where a ratio TAB (=SA/SB) of the outputs SA and SB iscalculated. This ratio TAB corresponds to the transmissivty of thesubstrate 1 in this portion.

The substrate 1 is adsorbed and held by a holder (not shown). Thisholder is fixed to a movable stage 6, and is movable disposed on a base7 in two-dimensional directions parallel to the pattern surface of thesubstrate 1. Although it is not illustrated, an encoder for measuring aposition of the movable stage 6 and a sensor for detecting a position ofthe substrate 1 are also disposed. In this signal processing system, themovable stage 6 is driven by a motor (not shown), the substrate 1 israster-scanned two-dimensionally along the pattern surface and at thesame time, whenever the position of the substrate 1 is varied by apredetermined amount, the ratio TAB of the outputs SA and SB of the twooptoelectronic detectors DA and DB is detected. By obtaining the ratioTAB as function of the two-dimensional position of the substrate 1, thetransmissivity distribution of the substrate 1 and non-uniformity(variation) of the transmissivity distribution are measured.

In order to compensate the non-uniformity of the transmissivitydistribution of the substrate 1 measured in this manner, the thin film 3shown in FIGS. 1A and 1B are formed on the surface (back surface) B ofthe substrate 1 using a film-forming apparatus shown in FIG. 3. Aevaporation substance (material of the thin film 3) discharged from aevaporation source 8 by heading or radiation of electron beam reaches ashield plate 9 disposed in the vicinity of the substrate 1. Only theevaporation substance which has passed through an opening 9 a reachesthe substrate 1, and a film is formed. At the time of this evaporation,the shield plate 9 is allowed to raster-scan two-dimensionally within aplane along the surface B of the substrate 1. Therefore, by changing thespeed of the raster scan in accordance with location within the surfaceB of the substrate 1 where the opening 9 a is located, it is possible toadjust a residence time of the opening 9 a at each of positions in thesurface B of the substrate 1. In this embodiment, by adjusting theresidence time of the opening 9 a, it is possible to adjust a. filmthickness distribution of the thin film 3 evaporated in the surface B ofthe substrate 1 to a desired distribution. In this embodiment, the filmthickness distribution of the thin film 3 is set to such a distributionas to compensate the non-uniformity of the transmissivity distributionof the substrate 1 itself measured as described above.

The forming method of the thin film 3 is not limited to theabove-described evaportaion method only, and a CVD (Chemical VaporDeposition) method or a sputtering method can also be used. Theformation of the film thickness distribution is not limited to themethod for controlling the growth itself of the film using the shieldplate 9 at the time of film formation, and it is possible to use amethod in which the film is previously formed with uniform thickness,the thin film is partially polished or ground, thereby varying thethickness distribution.

In the substrate 1 shown in FIG. 3 produced by the above-describedmethod, a light-shield film for forming the original pattern is formedon the pattern surface A opposed to the surface B on which the thin filmwas formed. This light-shield film is subjected to pattern cleaningusing an electron beam drawing apparatus or the like, thereby formingthe original pattern 2 shown in FIGS. 1A and 1B. With this arrangement,the reticle R shown in FIGS 1A and 1B is complete. The light-shield filmas the original pattern 2 is a thin film having absorbing or reflectingability, and its transmissivity need not always be 0, and thelight-shield film may be a so-called half-tone reticle using a filmhaving transmissivity of about 10% or less of course.

By mounting the reticle R completed in this manner to a projectionexposure apparatus, it is possible to expose a pattern of apredetermined layer of an electronic device.

FIG. 5 shows an essential portion of the projection exposure apparatusto which the reticle R is mounted. In FIG. 5, a wafer W is disposed on alower surface of the reticle R held on a reticle stage (not shown)through a projection optical system 42 of reduced magnification β (β is⅕, ¼ or the like). A photoresist is applied to a surface of the wafer W,and the surface is held such that it coincides with an image plane ofthe projection optical system 42.

In order to enhance the resolution in this embodiment, an F₂ laser(wavelength is 157 nm) is used as exposure light IL1, and kinds ofglasses which can be used as a refractor are limited with respect to theexposure light of such short wavelength. Therefore, acatadioptric systemor a reflection system may be used as the projection optical system 42instead of the catadioptric system. In the following explanation, a Zaxis is parallel to an optical axis AX1 of the projection optical system42, and plane rectangular coordinates perpendicular to the Z axis are Xaxis and Y axis. First, the wafer W is held on a sample stage 43 througha wafer holder (not shown), and the sample stage 43 is fixed on an XYstage 44. The XY stage 44 is driven based on coordinates measured bymoving mirrors 45mX and 45mY as well as corresponding laserinterferometers, thereby positioning the wafer W in X and Y directions.

A reference mark member 46 on which. reference marks 47A and 47B areformed is fixed on the sample stage 43, alignment sensors 41A and 41Bare disposed above alignment marks 24A and 24B formed such as tosandwich the original pattern 2 of the reticle R in the X direction.When the original pattern 2 is formed, the alignment marks 24A and 24Bare formed at the same time. In this case, the reticle R is aligned withthe sample stage 43 using the reference marks 47A and 47B, the alignmentmarks 24A and 24B and the alignment sensors 41A and 41B.

Thereafter, if superposition exposure is carried out, alignment of eachshot region 48 on the wafer W is carried out using a wafer alignmentsensor (not shown). Then, the shot regions 48 to be exposed on the waferW are sequentially positioned at the exposure position and then, byirradiating the original pattern 2 of the reticle R with the exposurelight IL1 by an illumination optical system (not shown), the originalpattern 2 is reduced with reduced magnification β as an image 27W andthe image 27W is exposed on the shot region 48. In this manner, thereduced image of the original pattern 2 is exposed in each shot regionon the wafer W and then, the wafer W is developed, process such asetching is carried out, and a circuit pattern of a certain layer of anelectronic device is formed in each shot region on the wafer W. Aftersuch pattern forming steps are repeated, bonding and dicing steps andthe like are carried out and the electronic devices are produced.

As a projection exposure apparatus for exposing the reticle R, areduction projection type exposure apparatus of scanning exposure typesuch as step and scan type.

The electronic devices are produced in this manner, in the reticle R ofthis embodiment, since the non-uniformity of transmissivity distributionof the substrate 1 itself of the reticle R is compensated by the thinfilm 3, it is possible to excellently maintain the uniformity of theline width of the circuit pattern transferred and formed from thereticle R, operation speed of the electronic device can be enhanced.

Further, it is possible to realize a lithograph using exposurewavelength of extremely short wavelength, i.e., lithography capable oftransferring extremely fine pattern. Such a lithography could not berealized conventionally because the transmissivity distribution of thesubstrate itself of the reticle is not uniform. Therefore, it ispossible to further increase the packing density of the electronicdevices and enhance the speed thereof.

Although the member for compensating the non-uniformity of thetransmissivity distribution of the substrate 1 of the reticle is thethin film 3 provided on the back surface B of the pattern surface A onthe substrate 1 in the above embodiment, the compensating member is notlimited to the thin film 3, and it is also possible to improve theuniformity by charging absorbent substance on the surface of thesubstrate 1 to lower the transmissivity of that portion. The chargingoperation may be carried out by irradiating the substrate 1 with ionwhich is accelerated by high voltage, or by evaporating substance to becharged on the surface of the substrate 1 and allowing the substance topenetrate into inside by annealing (heating). In this case also, theamount of substance to be charged is of course changed in accordancewith a position in the pattern surface of the substrate 1 in accordancewith the transmissivity distribution of the measured substrate 1 itself.

A portion of the substrate 1 having low transmissivity, the substrate 1itself may be polished and ground to enhance the transmissivity.

A second embodiment of the present invention will be explained withreference to FIG. 4.

FIG. 4 shows a reticle R1 of the second embodiment. In FIG. 4, as thesubstrate 1, a flat plate formed of quartz or synthetic quartz dopedwith a predetermined impurity is used. An original pattern 2A if formedon a pattern surface of the substrate 1 of this embodiment, a backsurface of the pattern surface is not formed with a thin film or thelike. In this embodiment, the original pattern 2A itself is used as amember for uniformizing the transmissivity distribution. That is, inthis embodiment also, like the first embodiment shown in FIGS. 1A and1B, the transmissivity of the substrate 1 itself is higher at itscenter, and becomes lower toward the periphery or outer side of thesubstrate 1. As shown in FIG. 4, a size (line width) itself of alight-shield pattern of the original pattern 2A to be formed is set suchthat a light-shield pattern existing at the center portion of thesubstrate 1 itself having high transmisslvity has a width dl thickerthan a designed value, and a light-shield pattern 22 existing at theperipheral portion of the substrate 1 itself having low transmissivityis thinner than the designed value (d2<d1). With this feature, since thetransmissivity distribution of the reticle R1 is uniformized as a whole,the line width of the circuit pattern to be transferred can beuniformized.

In the above embodiment, the transmissivity compensating member forcompensating the non-uniformity of the transmissivity distribution isprovided on the back surface (opposite surface from the pattern surface)of the substrate of the reticle or mixed in the substrate, but anothersubstrate (its material may be the same as the substrate of the reticle)which is different from the substrate of the reticle formed with thetransmissivity compensating member, and this member may be integrallyfixed to the reticle (the member may be brought into tight contact withthe reticle or a predetermined distance may be provided therebetween),or the other substrate may be in storage in the exposure apparatus in acorresponding manner to the reticle, an identification pattern (bar codeor the like) formed in the reticle may be read, and another substratecorresponding to the pattern may be disposed on the reticle stagetogether with the reticle.

The reticle is not limited to one comprising only the light-shield layermade of chromium (Cr), and the reticle may be a phase-shift reticle ofspacial frequency modulation type (Shibuya-Levenson type),edge-emphasizing type or half-tone type.

A use for the projection exposure apparatus using the reticle is notlimited to the projection exposure apparatus for producing thesemiconductor devices, and the projection exposure apparatus can widelybe applied to a projection exposure apparatus for liquid crystal forexposing a liquid display device pattern on a square glass plate, or aprojection exposure apparatus for producing a thin film magnetic head.The projection exposure apparatus can also be used for a reticle (mask)using a photolithography step using far ultraviolet rays (DUV rays) orvacuum ultraviolet rays (VUV rays) as exposure light. The magnificationof the projection optical system is not limited to the reduction system,and may be equal magnification or increased magnification.

A single wavelength laser in an infrared region or visible region lasedfrom a DFB semiconductor laser or fiber laser may be amplified with afiber amplifier doped with erbium (Er) (or both erbium and ytterbium(Yb), and a harmonic whose wavelength is converted into ultraviolet raysusing a non-linear optical crystal.

For example, if the lasing wavelength of the signal wavelength laser isin a range of 1.544 to 1.553 μm, eight times harmonic in a range of 193to 194 nm, i.e., ultraviolet rays having substantially the samewavelength as that of the ArF excimer laser can be obtained, and if thelasing wavelength is 1.57 to 1.58 μm, ten times harmonic in a range of157 to 158 nm, i.e., ultraviolet rays having substantially the samewavelength as that of the F₂ excimer laser can be obtained.

In the first embodiment, the transmissivity compensating member forcompensating the non-uniformity of the transmissivity distribution isused. However, when the transmissivity distribution of the reticle,i.e., the entire surface in the region on which the original pattern isto be formed is not uniformized even the transmissivity compensatingmember is used, the transmissivity is measured using a measuring systemshown in FIG. 2, the line width of the original pattern is partiallyincreased or reduced with respect to the designed value so that theremaining non-uniformity of the transmissivity distribution iscompensated. That is, the first and second embodiments may be combined.

When one surface of the substrate is reformed (by charging absorbentsubstance to the substrate surface or by polishing the substratesurface) to compensate the non-uniformity of the transmissivitydistribution, the surface of the substrate to be reformed is not limitedto the back surface B, and this surface may be pattern surface A or maybe both the surfaces A and B. The same can be said when the thin film inthe first embodiment is formed or the transmissivity compensating memberis formed on another substrate other than the substrate 1. When the thinfilm is formed on the pattern surface, the thin film may be formed afterthe original pattern is formed. Further, at least two of the pluralityof structure examples (formation of the thin film, formation oftransmissivity compensating member on another substrate other than thesubstrate 1, or reforming the substrate surface), or at least one of theplurality of structure examples and the second embodiment may becombined. The same can be said when the transmissivity compensatingmember is formed on another substrate other than the substrate 1. Thatis, when the transmissivity compensating member is formed, methods forforming the thin film, charging the absorbent substance to the substratesurface and the like may be combined. When the transmissivitycompensating member is formed on another substrate other than thesubstrate 1, the other substrate may be disposed on any of the patternsurface or the back surface of the substrate 1.

The transmissivity compensating member may be formed on the entiresurface of the reticle, or on a portion of the reticle, i.e., only aregion (pattern region) generally surrounded by the light-shield bandand on which the original pattern is formed. In the latter case, since awindow through which the exposure illumination light passes or region onwhich the alignment mark or the like is formed exists outside thepattern region in some cases. Therefore, it is preferable that at leastthese regions are formed with the transmissivity compensating membereven though the region is outside the pattern region.

In the projection exposure apparatus shown in FIG. 5, the illuminationdistribution in the illumination region on the reticle R irradiated withthe exposure light may be adjusted so that the transmissivitydistribution of the substrate 1 is compensated. At that time, an opticaldevice in the illumination optical system is preferably moved slightlyto distribute the illumination so that the illumination distribution inthe exposure region on the wafer which is conjugate with theillumination region with respect to the projection optical system 42.When an optical integrator (homogenizer) provided in the illuminationoptical system is a fly-eye lens, an element disposed at an injectionsurface side of the fly-eye lens is preferably moved slightly. A methodfor adjusting the illumination distribution to compensate thetransmissivity distribution of the substrate 1 may be used singly, ormay be combined with at least one of the first and second embodiments.

The forming method of the original pattern onto the substrate 1 when thereticle is produced is not limited to the method using the electronicdrawing apparatus, and may be a method using an optical type projectionexposure apparatus. In this case, the reticle is produced in thefollowing manner for example. First, a parent pattern obtained byenlarging an original pattern 1/α times is formed on design data(including image data), the parent pattern is divided by “N” to producepartial parent patterns, and using an electronic drawing apparatus (orlaser beam drawing apparatus or the like), the partial parent patternsare respectively rendered on glass substrates on which photoresistsformed with light-shield films are formed, and the development, etchingand the like are carried out to form N-number of master reticles. The1/α is reciprocal of reduced magnification a of an optical projectionexposure apparatus for producing reticles, and a is ¼, ⅕ or the like forexample. Using the optical projection exposure apparatus for producingreticles, reduced images of the partial parent patterns of the N-numberof master reticles are sequentially stitched and transferred onto thesubstrate 1 on which the light-shield film is formed and the photoresistis applied, development, etching and the like are carried out to formthe original pattern, and reticles are produced.

When the original pattern is formed using the optical projectionexposure apparatus, since each partial parent pattern is reduced a timesand projected, there is merit that drawing error of each partial parentpattern by the electronic drawing apparatus is reduced α timessubstantially. Further, a plurality of reticles are produced, thepatterns of the N-number of master reticles are only repeatedlytransferred. Therefore, the plurality of reticles can be produced atextremely low cost and in a short time and thus, semiconductor devicescan be mass-produced inexpensively.

The semiconductor device is produced through a step for designingfunction and performance of the device, a step for preparing a reticlebased on this design and the above-described embodiment, a step forpreparing a wafer from silicon material, a step for exposing the wafer(photoresist) with exposure illumination light through the reticleproduced by the above-described embodiment using the exposure apparatusshown in FIG. 5, thereby transferring the pattern of the reticle ontothe wafer, a step (including a dicing step, a bonding step and apackaging step) for assembling the device, an inspection step and thelike.

The illumination optical system constituted by a plurality of lenses andthe projection optical system are assembled into the projection exposureapparatus, these apparatuses including the reticle are opticallyadjusted, the reticle stage and the wafer stage comprising a largenumber of mechanical parts are mounted to the projection exposureapparatus, wires and tubes are connected, and all of them are totallyadjusted (electricity adjustment, confirmation of operation and thelike), thereby producing the projection exposure apparatus of thisembodiment. It is preferable to produce the projection exposureapparatus in a clean room where a temperature and a clean degree aremanaged.

The present invention is not limited to the above-mentioned embodiments,and the invention may, as a matter of course, be embodied in variousforms without departing from the gist of the present invention.Furthermore, the entire disclosure of Japanese Patent ApplicationNo.10-277274 filed on Sep. 30, 1998 including description, claims,drawings and abstract are incorporated herein by reference in itsentirety.

INDUSTRIAL APPLICABLILITY

According to the substrate for the photomask, or the first or secondphotomask of the present invention, since the transmissivitycompensating member is provided, even if the transmissivity distributionof the substrate itself is not uniform, the uniformity of thetransmissivity distribution is enhanced when it is irradiated with theexposure illumination light. At that time, according to the firstphotomask, there is merit that the thin film as the transmissivitycompensating member and the original pattern can easily be formedwithout mechanical interference.

According to the third photomask of the invention, the line width of theoriginal pattern is only controlled, and even if the transmissivitydistribution of the substrate itself is not uniform, high uniformity ofthe transmissivity distribution can be obtained when it is irradiatedwith the exposure illumination light.

In these cases, when the substrate is formed of quartz, quartz glass orquartz glass doped with a predetermined impurity, the substrate hasrelatively high transmissivity even with respect to light having shortwavelength of about 200 nm for example, and high uniformity oftransmissivity distribution can be obtained.

According to the first, second or third exposure method, the uniformityof the line width of the pattern to be formed on the pattern surfacesubstance.

According to the first, second or third or fourth producing method of adevice, since the photomask of the present invention or the exposuremethod of the invention is used, high uniformity of the illuminationdistribution can be obtained on the substrate to be exposed. Therefore,there is merit that the uniformity of the line width of the circuitpattern to be formed is enhanced, and advanced devices can be produced.

In the lithography using, as exposure wavelength, extremely shortwavelength which limits the kinds of optical material having excellenttransparent, if the photomask of the invention is used, thenon-uniformity of the transmissivity distribution of the substrateitself of the photomask is compensated, and the transmissivitydistribution can be uniformized over the entire photomask. Therefore, ascompared with the prior art, light of shorter wavelength can be used, anelectronic device can be formed more finely, the packing density thereofcan be increased, and the operational speed can be enhanced.

What is claimed is:
 1. A substrate for a photomask, on which an originalpattern is formed, comprising: a substrate formed of a material havingnon-uniformity of a transmissivity distribution; and a transmissivitycompensating member which is formed on the substrate and whichcompensates for the non-uniformity of the transmissivity distribution ofthe substrate.
 2. A substrate for a photomask as recited in claim 1,wherein a member selected from the group consisting of quartz, quartzglass, quartz glass doped with a predetermined impurity, sapphire andmagnesium fluoride is used as the material of the substrate.
 3. Asubstrate for a photomask as recited in claim 1, wherein thetransmissivity compensating member comprises a thin film provided on onesurface of the substrate, and a film thickness distribution of the thinfilm is set in accordance with the transmissivity distribution of thesubstrate.
 4. A substrate for a photomask as recited in claim 3, whereinthe thin film is made of a member selected from the group consisting ofsilicon dioxide, aluminum oxide, magnesium fluoride, aluminum fluorideand a metal thin film.
 5. A substrate for a photomask as recited inclaim 1, wherein the transmissivity compensating member is formed byreforming a portion of at least one surface of the substrate.
 6. Asubstrate for a photomask as recited in claim 1, wherein thetransmissivity compensating member is formed by providing anothersubstrate other than the substrate with a transmissivity distributionwhich substantially compensates for the non-uniformity of thetransmissivity distribution of the substrate.
 7. A photomask comprising:a substrate formed of a material having non-uniformity of atransmissivity distribution; a transmissivity compensating member whichis formed on one surface of the substrate and which compensates for thenon-uniformity of the transmissivity distribution of the substrate; andan original pattern formed on a surface of the substrate opposite to theone surface of the substrate.
 8. A photomask comprising: a substrateformed of a material having non-uniformity of a transmissivitydistribution; a transmissivity compensating member which is formed onone surface of the substrate and which compensates for thenon-uniformity of the transmissivity distribution of the substrate; andan original pattern formed on a surface of the substrate opposite to theone surface of the substrate, and having a line width which is made tobe different from a designed value in accordance with the transmissivitydistribution of the substrate provided with the transmissivitycompensating member.
 9. A photomask comprising: a substrate formed of amaterial having non-uniformity of a transmissivity distribution; and anoriginal pattern formed on a surface of the substrate, and having, inorder to compensate for the non-uniformity of the transmissivitydistribution of the substrate, a line width which is made to bedifferent from a designed value in accordance with the transmissivitydistribution of the substrate.
 10. A photomask as recited in claim 9,wherein a member selected from a group consisting of quartz, quartzglass, quartz glass doped with a predetermined impurity, sapphire andmagnesium fluoride is used as the material of the substrate.
 11. Anexposure method, comprising: illuminating a photomask including asubstrate formed of a material having non-uniformity of a transmissivitydistribution a transmissivity compensating member which is formed on onesurface of the substrate and which compensates for the non-uniformity ofthe transmissivity distribution of the substrate, and an originalpattern formed on a surface of the substrate opposite to the one surfaceof the substrate; and exposing a photosensitive object with light whichhas passed through the original pattern of the photomask.
 12. Anexposure method as recited in claim 11, wherein a line width of at leasta portion of the original pattern is made different from a designedvalue in accordance with the transmissivity distribution of thephotomask provided with the transmissivity compensating member.
 13. Anexposure method as recited in claim 11, further comprising adjusting anillumination distribution of the light on the photosensitive object inaccordance with the transmissivity distribution of the photomaskprovided with the transmissivity compensating member.
 14. An exposuremethod, comprising: illuminating a photomask including a substrateformed of a material having non-uniformity of a transmissivitydistribution and an original pattern formed on a surface of thesubstrate; exposing a photosensitive object with light which has passedthrough the original pattern of the photomask; and a adjusting anillumination distribution of the light on the photosensitive object inaccordance with the transmissivity distribution to compensate for thenon-uniformity of the transmissivity distribution of the photomask, whenthe photomask is illuminated.
 15. An exposure method, comprising:illuminating a photomask including a substrate formed of a materialhaving non-uniformity of a transmissivity distribution and an originalpattern formed on a surface of the substrate and having a line widthwhich is, to compensate for the non-uniformity of the transmissivitydistribution of the substrate, made to be different from a designedvalue in accordance with the transmissivity distribution of thesubstrate; and exposing a photosensitive object with light which haspassed through the original pattern of the photomask.
 16. A deviceproducing method comprising exposing the original pattern on thesubstrate onto a substrate for a device by illuminating the photomask asrecited in claim 7 with illumination light which has passed through thesubstrate.
 17. A device producing method comprising exposing theoriginal pattern on the substrate onto a substrate for a device byilluminating the photomask as recited in claim 9 with illumination lightwhich has passed through the substrate.
 18. A device producing methodcomprising exposing the original pattern on the substrate onto asubstrate for a device by illuminating the photomask as recited in claim9 with illumination light which has passed through the substrate.
 19. Adevice producing method, comprising transferring a device pattern onto asubstrate for a device using the exposure method as recited in claim 11.